Apparatus For Bi-Directional Power Switching In Low Voltage Vehicle Power Distribution Systems

ABSTRACT

A plurality of modules each including at least a pair of series connected power MOSFETs are configured between a plurality of DC voltage sources, and a plurality output terminals for connection to respective loads, are controlled for selectively applying power to the loads via time delay switching incorporating forward biased intrinsic diodes of the MOSFETs in a given current path during initial application of power to a load, whereby a predetermined period of time after turning on one of the series connected MOSFETs, the associated other MOSFET is turned on to shunt its intrinsic diode for reducing the resistance in the current path to maximize current flow. The configuration of the plurality of power MOSFETs is also controlled for selectively providing bi-directional current flow between said plurality of DC voltage sources.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Ser. No. 13/134,901 filed Jun. 20,2011, the contents of which are incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

The invention was made with U.S. Government support under Contract No.W56HZV-07-C-0095 awarded by U.S. Army Tank Automotive Command (TACOM).

FIELD OF THE INVENTION

The present invention relates generally to power distribution systems,and more particularly to low voltage high current switching controlsystems for connecting different DC power sources to one or more loads,particularly as used in vehicle power management systems but not limitedthereto.

BACKGROUND OF THE INVENTION

In known high current low voltage DC power distribution systems, such asthose used in military ground and aerial vehicles, for example (but notlimited thereto), a combination of electromechanical relays, contactors,circuit breakers and/or fuses, are employed to selectively distributepower to an associated vehicle's electrical devices or loads. Thevarious electrical components of the vehicle system are protectedthrough use of the fuses and/or circuit breakers. The power generatingdevices, and storage batteries employed in such vehicles are selectivelyswitched into connection with the various system components via the useof electromechanical relays and/or contactors, which in certain systemsmay provide bi-directional power control. However, suchelectromechanical switching devices present reliability problems due tomechanical wear, arching between relay contacts, deterioration fromvibration, and moisture exposure. Also, the mechanical contacts ofelectromechanical relays and/or contactors tend to bounce when activatedor deactivated, thereby generating high amplitude electrical noise inthe associated system. Also, in systems powering reactive loads thattend to draw high inrush currents when electrically activated, abruptelectrical relay contact closures fbr providing power to such devicestypically results in power surges. In addition, such prior systemstypically require a large amount of power to be applied to theelectromechanical relays and contactors, in order to insure themaintenance of high mechanical pressure between associated electricalcontacts for minimizing contact resistance. Also, the use in the priorsystems of manually operated switches and circuit breakers forces alayout, such as in vehicles, that provides easy accessibility to suchmanually operated components.

There is a present need in the state of art for high current low DCvoltage power distribution systems having bi-directional power controlcapability with improved reliability, and automonous and remoteoperational capability. The present invention provides a majorimprovement in enhancing the reliability of high current low DC voltagepower distribution systems employing bi-directional power control.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved high current low DCvoltage power distribution system.

Another object of the invention is to provide a solid-state high currentlow DC voltage power distribution system requiring low power operation,and offering high reliability, negligible electrical noise uponswitching, bi-directional power control, and the ability to limit themagnitude of inrush currents when applying power to reactive loads.

With these and other objects in mind, the present invention, in oneembodiment, includes a plurality of pairs of series connected powerMOSFETs modules arranged in a modified symmetrical “phase leg” switchingconfiguration. The MOSFET arrangement is not application specific and inthis embodiment has at least three inputs and at least one output to acommon bus or load. In application the inputs connect between powersources such as batteries and/or generators and devices or loads to bepowered by the system, whereby individual control signals areselectively provided to the gates of the individual ones of theplurality of pairs of MOSFETs, via programmable control means, for inone mode of operation providing initially reduced current flow to a loadthrough use of forward biased intrinsic diodes of the MOSFETs, followedby turn on of an appropriate one of the MOSFETs associated with theintrinsic diode(s) to provide increased current to an associated loadfrom a selected source of power. In a preferred arrangement, for eachsuccessive two of the plurality of pairs of series connected powerMOSFETs, an output MOSFET of one pair is connected in parallel to anoutput MOSFET of the following pair to reduce or minimize powerdissipation and current path resistances.

In another embodiment of the invention, in a first mode of operation aplurality of MOSFETs are configured for selective connection of at leastone or a combination of a primary battery, secondary battery, and motordriven generator for connection to an internal bus, and therefrom to atleast one device or load requiring the selective application of DCpower. The control system has means to tie any of the inputs to theMOSFET array together (i.e. primary and secondary batteries busses canbe connected together to provide backup capability in the event of abattery failure.) In this mode, a controller means is programmed tosense when the voltage output of the primary battery is higher than thatof the secondary battery, for initially turning on a selected firstMOSFET of a given series connected pair thereof, for permitting currentto flow from the primary battery through the turned on or activatedMOSFET, and through the forward biased intrinsic diode of a secondMOSFET of another pair thereof, into the secondary battery, and after adelay time, the second MOSFET is turned on for minimizing the resistancein the current path between the primary and secondary batteries tomaximize the current flow from the primary battery to the secondarybattery. In a second mode of operation, when the controller means sensesthat the voltage level of the secondary battery is greater than that ofthe primary battery, the controller means is operable for turning on thesecond MOSFET for permitting the current to flow from the secondarybattery through the intrinsic diode of the first power MOSFET into theprimary battery, and after a time delay to turn on the first MOSFET formaximizing the current flow from the secondary battery to the primarybattery. In a third mode of operation when the generator is operable forproviding DC power, the controller means includes means for sensing suchgenerator operation, and first operating a selected third MOSFET forpermitting charging current to flow from the generator through anintrinsic diode of a fourth MOSFET, and into the primary battery,whereby after a time delay the fourth MOSFET is turned on to minimizethe resistance in the current path between the generator and primarybattery to maximize the charging current flow therebetween. In a fourthmode of operation, the controller means is operable for turning on afifth MOSFET to permit current to flow from the generator through theintrinsic diode of a sixth MOSFET to provide a flow of current from thegenerator to the secondary battery, and after a predetermined time delayto turn on the sixth MOSFET transistor for maximizing the chargingcurrent flow from the generator to the secondary battery. The purpose ofthese modes is to provide a smooth power transition by firstestablishing a current path via closing a first MOSFET switch of aseries connected pair whose intrinsic diode opposes current flow toallow the diode of the associated second MOSFET switch to conduct, thusestablishing a current path. Once established, the second MOSFET switchis turned on to reduce the connection path power dissipation. Thereverse diode of the first MOSFET is required to block current to breakthe connections in the event one wishes to turn the system OFF or ifthere is an over current condition.

A relatively low voltage high current power distribution system includesnine pairs of MOSFETs connected between an internal bus and at least aprimary battery, secondary battery, and motor driven generator, andbetween the internal bus and at least one load or component requiringpower. Controller means including means for sensing the level of voltageoutput from the primary and secondary batteries, and from the generator,whereby the controller means is programmed to selectively operate thenine pairs of MOSFETs in a plurality of modes of operation. In the firstmode of operation, when the primary battery voltage level is higher thanthe secondary battery voltage level, a selected first MOSFET having areverse biased intrinsic diode is turned on for providing a current pathfrom the primary battery through the main current path of the firstMOSFET, and through the relatively higher resistance of a forwardintrinsic biased diode of a second MOSFET to the secondary battery,whereafter a desired time delay, the second MOSFET is turned on forreducing the resistance in the current path to maximize the flow ofcurrent from the primary battery to the secondary battery. In the secondmode of operation, when the voltage level of the secondary battery isgreater than that of the primary battery, the second MOSFET is turned onto establish a current path from the secondary battery through theintrinsic reverse diode of the first MOSFET through the primary battery,and after a desired time delay the first MOSFET is turned on forminimizing the resistance between the first MOSFET and the primarybattery to maximize the current flow from the secondary battery to theprimary battery. In a third mode of operation the controller means uponsensing operation of the generator, selectively turns on a third MOSFETfor permitting charging current to flow from the generator through thelow resistance main current path of the third MOSFET, and the intrinsicreverse diode of a fourth MOSFET to the primary battery, and after adesired time delay the fourth MOSFET is turned on to minimize theresistance in the current path for maximizing the flow of chargingcurrent from the generator to the primary battery. In a fourth mode ofoperation, when the generator operation is sensed, the controller meansis selectively operable for turning on a fifth MOSFET to establish acurrent path from the generator through an intrinsic reverse diode of asixth MOSFET to the secondary battery for charging thereof, and after adesired time delay, the controller means turns on the sixth MOSFET forminimizing the resistance in the current path to maximize the flow ofcharging current firom the generator to the secondary battery. In afifth mode of operation, upon the controller means sensing operation ofthe generator, the controller means is selectively operable for turningon a seventh MOSFET to establish a current path from the generatorthrough the intrinsic diodes of eighth and ninth MOSFETs to the internalbus, whereafter a tenth MOSFET is turned on for connecting a load to theinternal bus, causing an initial low magnitude of current to flow fromthe generator to the load, followed by a time delay period after whichthe eighth and ninth MOSFETs are turned on for minimizing the resistancein the current path, thereby maximizing the magnitude of current flowingfrom the generator to the load. In a sixth mode of operation, aneleventh MOSFET is turned on for establishing a current path from theprimary battery through the intrinsic diodes of twelfth and thirteenthMOSFET transistors and the main current path of the eleventh MOSFET,whereafter a fourteenth MOSFET is turned on for connecting the internalbus to a second load, to supply a relatively low magnitude of currentthereto, and after a predetermined time delay the twelfth and thirteenthMOSFETs are turned on for minimizing the resistance in the current pathand maximizing the magnitude of current flow from the primary battery tothe second load. In a seventh mode of operation, a controller means isoperable tbr turning on a fifteenth MOSFET to establish a current pathfiom the second battery through the intrinsic diodes of sixteenth andseventeenth MOSFETs and the main current path of the fifteenth MOSFET tothe internal bus, whereafter an eighteenth MOSFET is turned on toconnect the internal bus to a third load, thereby permitting arelatively low magnitude of current to flow from the secondary batteryto the third load. After a predetermined time delay period the sixteenthand seventeenth MOSFETs are turned on for minimizing the resistance inthe current path to maximize the magnitude of current flowing from thesecondary battery to the third load. In other modes of operation, thecontroller means is operable for turning on any desired combination ofthe tenth, fourteenth, and eighteenth MOSFETs, for connecting anycombination of the first through third loads to the internal bus. In yetother modes of operation, the controller means is operable forestablishing current paths for connecting any combination of thegenerator, primary battery, and secondary battery to the internal busfor selectively providing power to any combination of the first throughthird loads, and for selectively connecting the generator to either oneor both of the primary and secondary batteries for charging the same,while at the same time utilizing the generator to provide power to thevarious loads. The MOSFET configuration can be extended within practicallimits to include additional batteries, and/or generators, and toprovide power to more than three loads therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a prior power distribution system;

FIG. 2 is a block and circuit schematic diagram for one embodiment ofthe invention;

FIG. 3 is a logic network for comparing the voltage level of batteriesfor another embodiment of the invention; and

FIG. 4 is a logic diagram of a switching control network for yet anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In typical vehicle electrical systems, a generator battery set is usedfor electrical power. With the advent of sophisticated electronicequipment, the need for clean un-interruptible power has becomenecessary to operate electronics found on many Military ground and airplatforms. In such systems requiring “clean” power, it is often requiredto have a primary electrical system to operate the normal vehicle loads(i.e. vehicle starter, windshield wipers, lights, heaters, etc.) and asecondary battery (as a minimum) or generator—battery set to providepower for momentary power dropouts. A typical prior power distributionsystem 19 is shown in FIG. 1, and consists of three DC power sources 20,22, 24 that are routed to an internal bus IB1, and then to individualoutputs 26, 28, 30, 32 for load distribution. In this example, three DCpower sources are shown (although the concept can be reduced or expandedto any number desired), and include one motor driven DC generator 22,one primary battery 20, and one secondary or backup battery 24. Thepower system outputs are represented as high current outputs 28, 30, 32,respectively, and a low current output 26, for providing power to thevehicle system electrical loads.

The prior power distribution system 19 of FIG. 1 has two possible modesof operation which will now be described. Each operating modecorresponds to typical vehicle power systems. Note that these are themost common applications, and the approach can be adapted to otherspecific applications.

In Mode 1 operation, the primary battery 20 provides continuous power tothe internal bus IB1 and corresponding vehicle loads (not shown).Operation of the vehicle engine (not shown) energizes the DC generator22 and allows it to provide power to the internal bus IB1, and systemloads connected to output terminals 26, 28, 30, 32, respectively, whilecharging the primary battery 20. In Mode 1, the secondary battery 24serves as a reserve and can be connected if necessary (i.e. primarybattery 20 failure). This type of system is commonly used in largevehicles with two (or more) electrical systems.

Mode 2 operation is indicative of the type of electrical systems foundin smaller vehicles, and consists of one generator 22, a primary battery20, and secondary battery 24. In this system, the generator 22 operatesall vehicle loads and charges both the primary and secondary batteries20, 24. The secondary battery 24 is switched to the internal bus IB1,and keeps it powered when the voltage drops on the primary electricalsystem during drop outs or outages.

In both mode 1 and mode 2 power system operational modes describedabove, it is apparent that power must be able to flow from the generator22 bi-directionally to each battery 20, 24, and to various loads, tofacilitate power delivery and charging. The system must also be able toblock power to maintain necessary isolation between the power sources,and prevent pull downs of the internal bus IB1.

As previously indicated, prior known power distribution systems are forimplementing low voltage power architectures similar to those describedabove, and utilizes a combination of electromechanical relays,contactors, fuses, and switches or circuit breakers, such as shown inFIG. 1.

With further reference to the prior power distribution system 19 shownin FIG. 1, typical operation of this system will now be described.Whenever power contactor K3 is closed or energized, the primary battery20 is connected to the internal bus IB1. Typically, military typevehicles utilize 28 volts DC power systems, although other levels of DCvoltage may be used. In this example, assume that with power contactorK3 energized, and circuit breaker CB1 closed, the engine of theassociated vehicle can then be started, whereafter DC generator 22 isdriven by the motor. After the motor is started, power contactor K2 isenergized utilizing the output power from the generator to both providenecessary power to the vehicle, while at the same time charging theprimary battery 20. Depending upon the vehicle's power requirements atany given time, in this example, power contactor K4 is energized alongwith closure of circuit breaker CB2 to provide power to a load connectedto output terminal 28; power contactor K5 is energized along withclosure of circuit breaker CB3 to provide power to a load connected tooutput terminal 30; and power contactor K6 is energized along withclosure of circuit breaker CB4 to apply power to a load connected tooutput terminal 32. If excessive currency is drawn from primary battery20, fuse F3 will open to protect the battery from overload. Similarly,should excess power be drawn from the generator 22, fuse F2 will open toprotect the generator 22. In the event of failure of the primary battery20, power contact K1 is energized to insert secondary battery 24 intothe system and onto the internal bus IB1. Also, at times that a sensor(not shown) senses that the voltage of the secondary battery 24 dropsbelow a desired level, the contactor K1 can be energized to permit thegenerator 22 to charge the secondary battery 24 back up to the desiredvoltage level, whereafter power contactor K1 is opened or d-energized.

Although the prior power distribution system 19 of FIG. 1 provides powercontrol, it has several disadvantages. The operation of power contactorsK1 through K6 typically require a significant amount of power foroperation. This is necessary to maintain high pressure on the conductorcontact surfaces to minimize contact resistance. The components aremechanical in nature and are subject to mechanical wear, contaminants,moisture and vibration and electrical arcing. The abrupt switching ofthe contacts generates noise from contact bounce and from currenttransients as the sudden current switching excites the cable reactancein the system. The use of high current circuit breakers CB1, through CB3and fuses F1, F2, F3 also require manual intervention in the case of asystem fault. Several improvements have been made in the art byreplacing the circuit breaker/contactor output pairs (CB2, K4) withsolid-state relays using power MOSFETS, transistors or IGBTs. While thisapproach is proven and eliminates some of the problems associated withthe electromechanical components, most devices in the present art forlow voltage power distribution are unidirectional (i.e. power source toload) and are not capable of handling high currents. Many knowncomponents are optimized for high voltage distribution and create toomuch voltage drop and power dissipation for use in low voltage DCsystems.

The inventors conceived a low voltage high current DC power control anddistribution system, primarily for vehicle power distribution, thatincludes a power MOSFET array or matrix for providing high powerswitching, and bi-directional power control between DC sources of power,along with unidirectional high current control of power outputs tovarious loads. The DC power sources particularly include batteries, andmotor driven generators. FIG. 2 shows a DC power distribution system 21that includes a number of embodiments of the present invention that willbe described in further detail below. It should be noted that althoughthe DC distribution or power control system 21 is shown to include as DCpower sources a primary battery 20, a motor driven DC generator 22, anda secondary battery 24, each being configured along with the switchingnetwork to at different times provide power to three loads connected tooutput terminals 40, 42, and 44, respectively, it is not meant that thesystem be so limited, and can be expanded to include additional DC powersources, and accommodate more than three loads or devices requiring DCpower. Expansion of the present DC power control system 21 is limitedonly by practical considerations within the present state-of-the-art.

With further reference to the DC power control and distribution system21 of FIG. 2, in a preferred embodiment for a low voltage high currentapplication the power MOSFET matrix includes a plurality of dual powerTrench MOSFET modules 1, 7A; 2, 7B; 3, 8A; 4, 8B; 5, 9A; 6, 98; 10, 13;11, 14; and 12, 15. However, the invention is not meant to be limited toTrench MOSFET devices, whereby any power MOSFET having an intrinsicsource drain body diode that can handle a given application's powerrequirements can be used for the various embodiments of the invention.Also included is a controller 23. To facilitate the understanding of theoperation of the present system 21, the intrinsic reverse diodes orsource-drain body diodes for each of the MOSFET devices are also shown.These source-drain body diodes include D1 through D6, D7A through D9A,D7B through D9B, and D12 through D15. Note that the aforesaid diodes areindicative of the direction of blocking current flow when theirassociated MOSFET is turned off. As will be further explained, in orderto implement a hi-directional switching capability, each power path ofthe matrix of MOSFETs of system 21 includes back-to-back diodes. Theinventors further recognized in conceiving the present invention thateach of the aforesaid power MOSFETs are operable in three modes, thefirst being a non-conductive mode, a second being a mode where currentflows through an associated source-drain body diode, and a third moderesponsive to a gate signal for turning on the MOSFET to provide a lowresistance connection between the associated source drain connectionsthereof, shunting the associated body diode. In one application of thepresent invention, the aforesaid dual power Trench MOSFET modules wereprovided by VMM 1500-0075X2 modules, manufactured by IXYS Corporation(Milpitas, Calif. 95035). Each such IXYS dual power MOSFET moduleincludes a pair of series connected Trench MOSFETs, each of which israted at 75 volts, 1500 amps, and each has when conductive adrain-source resistance of 0.38 milliohms. The present inventors chosethis component in view of its compatibility with 28 volts vehiclesystems, and the requirement that the system 21 be capable of handlingat least 500 amp currents. However, as previously mentioned, this choiceof component is not meant to be limiting, for the present invention canbe realized using other individual power MOSFETs, and power MOSFETpackages having different voltage and current ratings. It should befurther noted that this choice of component for the particularrequirements of one application for the DC power distribution system 21provided an extremely compact switching array having minimal space orvolume requirements, providing via each of the associated MOSFETswitches a very low voltage drop, low power dissipation, and highcurrent operation. Note further that each of the selected dual powerMOSFET modules include three pairs of Trench MOSFETs, each pair ofTrench MOSFETs being connected in pairs relative to their channels,whereby only such module is necessary for providing pairs of MOSFETS 10through 15, as shown in FIG. 2, for example. As indicated, the presentinventors chose to use time delay switching in the switching matrixhaving 100 millisecond delays, but such delay is not meant to belimiting. Also, in one embodiment the controller 23 includes afield-programmable gate array (FPGA) programmed to provide controlsignals through use of included analog circuitry, logic networks,analog-to-digital converters, and so forth.

Operation of the power distribution and control system 21 will now bedescribed. Note that in FIG. 2 the gate, source, and drain connectionsfor each of the MOSFETs shown are designated by S, D, and G,respectively. Also the controller 23 provides control signal lines C1through C18 for connection to the gates of the aforesaid MOSFETs, 1through 6, 7A, 71, 8A, 8B, 9A, 9B, and 10 through 15, respectively.Controller 23 causes control lines C1 through C6 to go high to turn onMOSFETs 1 through 6, respectively; C7 through C12 to go high to turn onMOSFETs 7A, 7B, 8A, 8B, and 9A, 9B, respectively; and C13 through C18 togo high to turn on MOSFETs 10 through 15, respectively. The primarybattery 20, secondary battery 24, and DC generator 22 are connected tocontroller 23, as shown. Note also in this application, referencedesignations C1 through C18 are used to designate either a controlsignal line, or an associated control signal with the same designation,which when “high” turns on its associated MOSFET. In a first embodimentof the invention, the primary battery 20 is initially connected in arelatively high resistance current path via diodes D7A, D7B of MOSFETs7A, 7B, respectively, to the drain of MOSFET 10, whereby when controller23 provides a gate signal C13 to the gate of MOSFET 10, the latter isturned on or energized to provide a relatively low resistance currentpath for connecting the primary battery to internal bus IB2. Note thatthe forward bias resistance of all of the aforesaid source-drain bodydiodes of the IXYS MOSFETs is typically dependent on the magnitude ofcurrent, and is typically less than 2.5 milliohms for the aforesaid IXYSTrench MOSFETs. After MOSFET switch 10 is turned on, either simultaneouswith such turn on or after predetermined phase-lag or time delay (100ms, for example), control signals C7, and C8 can be applied to the gatesof MOSFET switches 7A 7B, respectively, for connecting their energizedchannel resistances in parallel to minimize the resistance of thecurrent path from primary battery 20 to the internal bus IB2 (theparallel channel resistances will total about 0.19 milliohms when usingthe aforesaid IXYS Trench MOSFETs). Such action completes a lowresistance current path from primary battery 20 to the internal bus IB2,whereby the total resistance of this current path will be the sum of theseries channel resistances of MOSFETs 7A. 7B and 10, or about 0.57milliohms. Note further that if control signal C16 is present, MOSFET 13will be turned on to apply the primary battery 20 to a load connected tooutput terminal 44. Note further that where required, time delayswitching can be utilized to first allow current to pass through theintrinsic diode D7B, followed by turning on MOSFET 7B at a predeterminedtime later, such as 100 milliseconds later, for example, for shuntingdiode D7B with the low resistance channel thereof in an energized state.

The MOSFET switches 13 through 15 are configured to act as outputswitches, for controlling the application of power to loads connected tooutput terminals 44, 42, and 40, respectively, the DC power beingprovided from the internal bus IB2. The MOSFET switches 10 through 12are configured to be analogous to main circuit breakers, wherebycontroller 23 is operative to terminate control signals C13, C14, and/orC15, in the event of overload current or excessive current flowingthrough MOSFETs 10 through 12, respectively, to the internal bus IB2.Such control is provided either individually or in some combination inaccordance with the operation of MOSFETs 10 through 12, at any giventime. Note that when MOSFETs 10 through 12 are turned off, theirassociated intrinsic diodes D10 through D12, respectively, block theflow of current from primary battery 20, DC generator 22, and secondarybattery 24, respectively to the internal bus IB2. Similarly, when theoutput MOSFET switches 13 through 15 are turned off, their associatedintrinsic diodes D13, D14, and D15, respectively, block the flow ofcurrent from the internal bus IB2 to output terminals 44, 42, and 40,respectively.

When system 21 is employed for providing power to a vehicle, typicallythe primary battery 20 with at least MOSFETs 7A, 7B, and 10 turned on,the vehicle engine is started. The engine (not shown) then operates DCgenerator 22 for providing DC power to the vehicle systems andrecharging the primary and/or secondary batteries 20, 24, respectively,as required, and as will be explained in further detail. Typically, theDC generator 22 when energized has a higher DC output voltage thanbatteries 20, 24, respectively, whereby if this condition is not true atany given time, a sensing circuit (not shown) will disconnect thegenerator and switch to battery operation.

Upon operation of the DC generator 22, the controller 23 is operativefor turning on the aforesaid MOSFET switches in many differentcombinations, depending upon the vehicle requirements, and sensedoperating conditions at any given time. For example, the magnitude ofcurrent flowing through any current path to a load can be monitored viaa current sensor, such as a Hall-effect sensor (not shown) forprogramming the controller 23 to turn off any operative one of MOSFETs10 through 12, in the event of an overload condition, as previouslymentioned. With the DC generator 22 operative, controller 23 can beprogrammed to apply control signal C14 to MOSFET 11 to turn it on, whileinitially retaining MOSFETs 8A and 8B de-energized, whereby a relativelylow magnitude of current can flow from DC generator 22 through theintrinsic diodes D8A and D8B, and through the channel or main currentpath of MOSFET 11 to the internal bus 18B2. Controller 23 can beprogrammed to after a time delay of 100 milliseconds from the time ofturning on MOSFET 11, for example, to apply control signals C9 to thegate of MOSFET 8A, and C10 to the gate of MOSFET 8B, to turn them on,for minimizing the current path resistance between the DC generator 22and the internal bus IB2. With the generator connected to the internalbus IB2, controller 23 can be programmed to apply control signals C16through C18, to the gates of MOSFET switches 13 through 15,respectively, in any desired combination for powering loads connected tooutput terminals 44, 42, and 40, respectively.

When the DC generator 22 is operative for providing power to theinternal bus IB2, as previously indicated, controller 23 can beprogrammed to turn on MOSFETs 7A, 7B, and 10 for charging primarybattery 20 from the DC generator 22 via internal bus IB2. Alternatively,for a more direct charging path, MOSFET switches 2 and 3 can be turnedon, with 7A and 7B turned off, for charging primary battery 20 from DCgenerator 22.

Note further that in the switching matrix configuration of system 21,for one embodiment of invention, MOSFET switches 7A and 7B, 8A and 8B,and 9A and 9B are individually or in any combination respectively turnedon together or turned off together, and are thereby operative asindividual MOSFET switch pairs, respectively. As described for MOSFET 7Aand 7B, when each aforesaid pair are turned on their respective channelsare connected or parallel thereby minimizing the associated current pathresistance.

When controller 23 senses that the primary battery 20 has a voltagelevel below a predetermined operating level, MOSFETs 7A, 7B, and 10 areturned off, and MOSFETs 9A, 9B, and 12 are turned on, for connecting thesecondary battery 24 to the internal bus IB2. In operating with theprimary battery 20, time delay switching can be utilized, whereby firstMOSFET switch 12 is turned on with MOSFET switches 9A and 9B turned off,whereby a relatively high resistance current path will be establishedfrom secondary battery 24, through the intrinsic diodes D9A and D9B, andthe channel of MOSFET 12 to the internal bus IB2, whereby 100milliseconds later (in this example), controller 23 operates to turn onMOSFET switches 9A and 9B, for minimizing the resistance of the currentpath between the secondary battery 24 and internal bus IB2.

The MOSFET switching matrix of system 21 is operable via a controller 23for providing bi-directional current control between primary battery 20,and secondary battery 24, as immediately described. As previouslymentioned, in the prior art connection between the primary and secondarybatteries 20, 24, respectively, is typically provided by closure ofelectromechanical contactors or relay contacts, whereby the direction ofcurrent flow is dependent on the level of the battery voltages of thesystem at the time of contact closure. Such abrupt circuit connectiontypically results in high inrush currents, and electrical noise producedfrom the electromechanical contacts. As will be explained, the presentinvention overcomes these problems by first sensing the relative levelsof voltage of the primary battery 20 and secondary battery 24 before anyconnection therebetween, and directly controlling MOSFET switches 1 and6 of system 21 in a manner that provides for current flow between thebatteries to be first minimized by flow-through associated intrinsicdiodes, followed by maximizing the current flow through turn on of theMOSFET associated with the forward biased intrinsic diode to minimizethe resistance in the current path therebetween. More specifically, inthis example, the logic network of FIG. 3 is built into controller 23for comparing the voltage levels of primary battery 20 and secondarybattery 52 at any given time. The logic network 51 operates by supplyingthe voltage levels of primary 20 and secondary battery 24 via A/Dconverters 53, 55, respectively, to individual inputs of a XOR(Exclusive OR) gate 54. The primary voltage level from A/D 53 is alsoapplied to an input of an AND gate 58, with the secondary voltage levelalso being applied from A/D 55 to an individual input of another ANDgate 60. The output of XOR gate 54 is applied through a delay logic 56to individual inputs of AND gate 58 and 60. When the output of AND gate58 is high, and that of AND gate 60 is low on signal lines 64, 68,respectively, the secondary voltage level is less than the primaryvoltage level. When the output of AND gate 60 is high on signal line 68,and low signal line 64, this is indicative of the secondary voltagebeing greater than the primary voltage level. When the output signalsfrom And gate 58 and AND gate 60 are each low, the low signals beingapplied as inputs to OR gate 62, the latter operates to apply a highsignal on signal line 66 indicating that the primary voltage level isequal to the secondary voltage level.

The controller 23 further includes a control logic network 65 as shownin FIG. 4, for controlling the sequence of turn-on of MOSFETs 1 and 6,as will be described. As shown in FIG. 4, the logic network 65 includesan OR gate 74 receiving individual digital input signals from sensingcircuitry (not shown) indicative of the voltage level of the primarybattery 20 and secondary battery 52 having at least one at anoperational level, with the output from OR gate 74 being applied to anindividual input of an AND gate 76. An enable EN signal is applied tothe other input of AND gate 76, the output of which goes high uponreceiving high input signals. The output of AND gate 76 is connected toindividual inputs of AND gates 78, 80, and 82. AND gate 78 also hasindividual inputs connected to the output line 66 of OR gate 62, and anoverride line 70. And gate 80 also has individual inputs connected tothe output line 68 from AND gate 60, and an override signal line 70. ANDgate 82 also has individual inputs connected to an override line 70, andto output line 64 from AND gate 58 of logic 51. The output of AND gate78 is connected to individual inputs of OR gates 88 and 90,respectively. The output of AND gate 80 is connected directly to anindependent input of OR gate 88, and through a delay 84 to anindependent input of OR gate 90. AND gate 82 is connected directly to anindependent input of OR gate 90, and through a delay 86 to anindependent input of OR gate 88. When the output of OR gate 88 is high,control line C1 goes high for turning on MOSFET 1 of system 21, and whenthe output of OR gate 90 is high, control line C6 goes high for turningon MOSFET 6 of system 21. More specifically, at times that it isnecessary to connect primary battery 20 to secondary battery 24, whentheir voltage levels are equal, the logic networks 51 and 65 of FIGS. 3and 4, respectively, cause MOSFET switches 1 and 6 to turn onsimultaneously for directly connecting the batteries 20, 24 to oneanother via a minimum resistance current path. When it is sensed thatthe level of the voltage for the primary battery 20 is higher than thatof the secondary battery 24, control signal line C1 goes high, withcontrol signal line C6 low, for turning on MOSFET switch 1, therebyconnecting primary battery 20 through the low resistance channel or maincurrent path of energized MOSFET 1, and the intrinsic diode D6 of MOSFET6 to secondary battery 24, thereby initially establishing a relativelyhigh resistance current path therebetween. After a predetermined delayperiod, 100 milliseconds in this example, control signal line C6 fromthe output of OR gate 90 will go high for turning on MOSFET 6, forestablishing a relatively low resistance path between batteries 20 and24. Yet in another mode of operation, when the level of voltage of thesecondary battery 24 is greater than that of the primary battery 20,logic networks 51 and 65 are operative for causing the output line C6 ofOR gate 90 to go high for turning on MOSFET switch 6, for connecting thesecondary battery 24 through the low resistance main current path ofMOSFET 6, and the relatively high resistance of intrinsic diode D1 ofMOSFET 1, to the primary battery 20, whereby after a delay period of 100milliseconds, in this example, the output of OR gate 88 goes high forcausing signal line C1 to go high to turn on MOSFET switch 1, forestablishing a substantially low resistance current path betweenbatteries 20 and 24. In this manner, bi-directional current flow can beprovided between batteries 20 and 24, depending upon the voltage levelsof each at the switching time.

Table 1, as shown below, is illustrative of examples of six modes ofoperation of system 21, namely Modes I through VI, for DC voltage sourceto output switching.

TABLE 1 Pri. Sec. Gen. MOSFETs Switching/Operation State Mode Step Batt.20 Batt. 24 22 Condition And Control Line dly = time delay ~0.1 sec I aActive N/A Off Pri. Batt. 20 to Int. 10 (ON) dly 7A, 7B (ON) dly Bus.IB2 b Active N/A Off Int. Bus. IB2 to 13 (ON) dly 14 (ON) dly 15 (ON)Outputs 40, 42, 44 II a N/A Active OFF Sec. Batt. 52 to Int. 12 (ON) dly9A, 9B (ON) Bus. IB2 b N/A Active OFF Int. Bus. IB2 to 13 (ON) dly 14(ON) dly 15 (ON) Output 40, 42, 44 III a N/A N/A Active Gen. 22 Activelyto 11 (ON) dly 8A, 8B (ON) Int. Bus. IB2 b N/A N/A Active Int. Bus. IB2to 13 (ON) dly 14 (ON) dly 15 (ON) Outputs 40, 42, 44 IV a Active N/AOFF Pri. Batt. 20 to bus 10 (ON) dly 7A, 7B (ON) dly prior to start bActive N/A Active Gen. 22 Start/Gen 22 11 (ON) dly 10 (OFF) dly 8A, 8BTo Bus. IB 2 c Active N/A Active Gen. 22 to charge Pri. 3 (ON) dly 2(ON) dly Batt. 20 d Active N/A Active Int. Bus. IB2 to 13 (ON) dly 14(ON) dly 15 (ON) Outputs 40, 42, 44 V a N/A Active OFF Sec. Batt. 52 tobus 12 (ON) dly 9A, 9B (ON) dly prior to start b N/A Active Active Gen.22 Start/Gen 22 11 (ON) dly 12 (OFF) dly 8A, 8B To Bus. IB 2 c N/AActive Active Gen. 22 charge Sec. 4 (ON) dly 5 (ON) dly Batt. 52 d N/AActive Active Int. Bus. IB2 to 13 (ON) dly 14 (ON) dly 15 (ON) Outputs40, 42, 44 VI a Active Active OFF Pri. Batt. 20 to bus 10 (ON) dly 7A,7B (ON) dly prior to start b Active Active Active Gen. 22 Start/Gen 2211 (ON) dly 7A, B (OFF) dly 8A, 8B To Bus. IB 2 c Active Active ActiveGen. 22 charge Pri. 3 (ON) dly 2 (ON) dly Batt. 20 d Active ActiveActive Gen. 22 charge Sec. 4 (ON) dly 5 (ON) dly Batt. 52 e ActiveActive Active Int. Bus. IB2 to 13 (ON) dly 14 (ON) dly 15 (ON) Outputs40, 42, 44

Table 2, as shown below, illustrates operational Modes VII through IXfor primary battery 20 to secondary battery 24 connections.

TABLE 2 Pri. Sec. Gen. MOSFETs MOSFETs Mode Step Batt. 20 Batt. 24 22Battery Voltage Levels Turned On Turned On VII a Active Active N/A Pri.Batt. 20 > Sec. Batt. 52 1 dly 6 b Active Active N/A Pri. Batt. 20 toInt. Bus. IB2 10 dly 7A, 7B VIII a Active Active N/A Pri. Batt. 20 <Sec. Batt. 52 6 dly 1 b Active Active N/A Pri. Batt. 20 to Int. Bus. IB210 dly 7A, 7B IX a Active Active N/A Pri. Batt. 20 = Sec. Batt. 52 6.1dly dly b Active Active N/A Pri. Batt. 20 to Int. Bus. IB2 10 dly 7A, 7B

Note that Tables 1 and 2 do not show all possible switching modes, otherof which are believed apparent from the above description of operation.Further note that in Tables 1 and 2 the sequence steps for each mode arefrom left to right starting at “a,” proceeding to the end, then startingat “b” to the end, and so firth.

From the description of operation given above, it has been shown thatthe low voltage high power distribution system 21 is operative forproviding switching with minimized electrical noise development comparedto prior electrical mechanical switching systems. Also, the presentinvention provides for substantially reducing high magnitude inrushcurrents when delivering power to various DC loads, or interconnectingbattery power sources of the system together, for establishment ofcurrent paths that initially include the resistance of an intrinsicdiode or pair of intrinsic diodes in a desired current path, followed bya predetermined delay for turning on associated MOSFET switches tominimize the resistance in the current path for maximizing the magnitudeof current flow therethrough.

Although various embodiments of the present invention have beendescribed in detail above, they are not meant to be limiting. Those ofskill in the art may recognize certain modifications to the embodimentstaught herein which modifications are meant to be covered by the spiritand scope of the appended claims. For example, the switching system ofFIG. 2 can be expanded to include any number of DC sources of power, andany number of loads or output terminals to a practical limit.

What is claimed is:
 1. In a low voltage high current DC powerdistribution system, the method comprising the steps of: connecting anoutput of a primary battery to a drain electrode of a first power MOSFETswitch; connecting a source electrode of said first power MOSFET switchto a source electrode of a second power MOSFET switch; connecting adrain electrode of said second power MOSFET switch to an output of asecondary battery; comparing the voltage level of said primary batteryto that of said secondary battery; and operating a controller in a firstmode to sense when the voltage level of the primary battery is greaterthan that of the secondary battery, for applying a control signal to agate electrode of said first power MOSFET switch for turning it on toconnect said primary battery through the relatively high resistance of abody diode of said second power MOSFET switch to said secondary battery,and after a predetermined period of time applying a control signal to agate electrode of said second power MOSFET switch to turn it on to shuntits body diode with its relatively low resistance channel, forsubstantially reducing the resistance in the current path between saidprimary and secondary batteries.
 2. The method of claim 1, furtherincluding the step of: operating said controller in a second mode tosense when the voltage level of the secondary battery is greater thanthat of said secondary battery, for applying a control signal to a gateelectrode of said second power MOSFET switch for turning it on toconnect said secondary battery through the relatively high resistance ofa body diode of said first power MOSFET switch to said primary battery,and after a predetermined period of time applying a control signal to agate electrode of said first power MOSFET switch to turn it on to shuntits body diode with its relatively low resistance channel, forsubstantially reducing the resistance in the current path between saidprimary and secondary batteries.
 3. The method of claim 2, furtherincluding the step of: operating said controller in a third mode tosense when the voltage levels of the primary and secondary batteries areequal, for simultaneously applying control signals to the gateelectrodes of said first and second power MOSFET switches for turningthem on to establish a relatively low resistance current path betweensaid primary and secondary batteries.